Generator and power plant therefor



March 1941' A. w. KIMBALL GENERATOR AND POWER PLANT THEREFOR Filed April26, 1940 u x 1\ \l 1 \1 //l w \\\w INVEN.TOR W X12254,

ATTORNEY m w /I\ WITN ESSES:

Patented Mar. 18, 1941 UNITED STATES PATENT oFFIcE Albert W. Kimball,Forest Hills, Pm, assignor to Westinghouse Electric 42 ManufacturingCompany, East Pittsburgh, Pa'., a corporation of PennsylvaniaApplication April 26, 1940, Serial No. 331,745

6 Claims.

My present invention relates to a self-regulating direct-currentcommutator-type generator of a special type having a relatively flatvolt-, age-characteristic from very low loads up to somewhere in theorder of of the normal load which it may be called upon to carry, and avoltage-characteristic which is drooping with increased load-currentthereafter, and my invention has more particular relation to a powerplant including a prime mover, such as a gasoline engine, for drivingsuch a generator. The particular application for which my invention wasdesigned was for an anti-aircraft searchlight generator which isrequired to operate, most of the time, at a very lowload, such as12amperes at 105 volts, called the listening load, during which time'thegenerator-output is utilized merely to energize certain apparatusassociated with the searchlight. When the presence of aircraft isdetected, however, a powerful searchlight is turned on, at which timethe generator or power plant is called upon to deliver a short-timepeak-load of approximately 325' amperes, which reduces as the arc isdrawn, and stabilizes at approximately 162 amperes, at approximatelyvolts. However, surges may occur which cause the current to vary withinthe range of 122 to 202 amperes. For stable operation of theSearchlight, it is necessary for the voltage to decrease approximately1%, volts for each 10 amperes increase in load. Therefore thecorresponding voltage-range must be approximately to 95 volts.

Heretofore, the equipment necessary to supply this service has includeda special current-responsive solenoid, picking up at approximately 70amperes and dropping out at approximately 35 amperes, for so changingthe spring-tension on the engine-governor'as to increase the speed, froman idling speed of 900 R. P. M., during listening operations, to a fullspeed of 1200 R. P. M. when the searchlight is energized. At the sametime, in these previous. installations, it was necessary to provide avoltage-regulator, or special voltage-control means in the generator, sothat it would maintain acceptable voltage-conditions under the-variousconditions of loading.

The principal object of my present invention is to dispense with allcontrol-means or regulators, except the engine governor and the shuntfield rheostat, when a single-speed power plant is used, that is, onewhich does not change the governor-setting when changing from low-loadto high-load conditions. Such a power plant eliminates both thespeed-changing solenoid for the engine and the voltage-regulator for thegenerator, a thing which was heretofore believed to be impractical whilestill obtaining the necessary operating-characteristics from thegenerator. I now utilize a prime mover having an approximately constantspeed, with a speed-characteristic which droops, with load, by only theamount which is necessary for stable operation. Thus,

the listening-load speed can be approximately 1050 R. P. M., while thearc-load speed is approximately 1000 R. P, M. This materially simplifiesthe operation of the power plant, but it imposes a very specialoperating-condition on the generator, which has required special design,in order to cause the inherent voltage-regulation of the generator,without the assistance of any voltage-regulator, to give the requiredvoltagecharacteristic. 1

The principal object of my present invention is to provide aself-regulating generator having certain special design-features, incombination, as will be subsequently described and claimed, wherebythese special voltage-characteristics are obtained, and to provide apower plant including such a generator, the generator being providedwith a cumulative series winding for compensating for the droop in thespeed-characteristic of the prime mover and for compensat ing for theinternal voltage-drop of the generator.

With the foregoing and other objects in view, my invention consists inthe apparatus, combinations, circuits, systems and.methods hereinafterdescribed and claimed, and illustrated in the accompanying drawing,wherein Figure 1 is a fragmentary transverse sectional view through agenerator embodying my invention;

,Figs. 2, 3, 4 and 5 are explanatory'diagrams which will be referred toin the explanation of the special design-features relating to the mainpole-pieces of the generator, and

Fig. 6 is a diagrammatic view of the power plant, and of thecircuit-connections of the generator,

. As shown in Fig. 1, the illustrative form of embodiment of mygenerator comprises a statormember or field member, comprising an outerframe-ring or yoke-member I of magnetizable material such as a rolledslab of steel, four main pole-pieces 2 of magnetizable material, such assheet-steel laminations which are held together by rivets 3, and tourinterpole-pieces 4 which are also of magnetizable material which may besimilar to the material 01' which the main pole pieces 2 areconstructed. Each of the main pole-pieces 2 carries a self-excited shuntcoil 5 and a cumulative series coil 6, while each of the interpolepiecescarries a series-connected commutating or interpole-coil 1.

The generator is also provided with a commutator-type rotor-membercomprising a slotted magnetizable armature-core B carryingarmature-windings 9 and mounted upon a shaft Hi. In common with theother commutator-type direct-current generators, and as diagrammaticallyindicated in Fig. 6, the armature-windings 9 are connected to acommutator which is diagrammatically represented, in Fig. 6, as thesurface of the armature 8, current being conducted to and from thecommutator by means of brushes M.

In accordance with my invention, special design-features are embodied inboth the main pole-pieces 2 and the commutating or interpolepieces 4.Each main pole-piece 2 is provided with a pole-face portion or surfacel4 which is spaced, from the armature-core 8, by an air-gap which, inaccordance with my present invention, is tapered, as indicated at [5.Each main polepiece 2 is also provided with a first pole-face tip IS inwhich the armature reaction produces a cumulative magnetomotive force,and a second pole-face tip H in which the armature reaction produces adifferential magnetomotive force. This corresponds to a certainpredetermined direction of rotation of the armature, as indicated by thearrow [8 in Fig. 1.

In accordance with my invention, the large end of the tapered air-gapI5, under each of the main pole-pieces 2, is under the first-mentioned,or cumulative-flux, pole-face 16. Also, in accordance with my invention,the first-mentioned or cumulative-flux tip I6 is of an unusually largesectional area, as compared to the more common generator-designs, so asto have sufiicient crosssection, in radial planes, to be substantiallyunsaturated for small load-currents; or for currents up to, say of theorder of 60% of the normal load,

by which I mean a current-range of from say 40%, to say 80% o someloading-condition which I herein designate as the normal load, or evensomewhat more or less than these limits. Also, in accordance with mypresent invention, the second-mentioned, or differential-flux, pole-tipI1 is specially designed so that it will be substantially saturated atno-load, and at small loadcurrents, and even up to rather substantialloadcurrents of approximately 60% load, where the demagnetizing armaturereaction is very considerable, in this pole-tip H. In order to make thedifferential-flux pole-tip l1 saturate, its effective cross-sectionsmust be reduced or restricted, by any suitable means, such as providinga hole l8 therein, as shown in Fig. 1, or by any equivalent means forreducing the effective cross-section of the magnetizable material whichcarries flux in a circumferential direction in said pole-tip II.

In accordance with my invention, the interpole-piece 4 is speciallydesigned so that it will include therein a section of such reducedcrosssection as to saturate at very small currents, such,-

for example, as 30 amperes, in the illustrative embodiment of myinvention. This reduced-section region of each interpole-piece 4 may beprovided in any convenient manner or means, the illustrated meansconsisting of a special mounting, at .the rear end of theinterpole-piece 4, where it abuts against th frame-ring I of thegenerator. Thus, as shown in Fig. 1, the back end of the interpole-piece4 is separated from the frame 1 by means of non-magnetic shims orspacers 20 providing, in effect, an air-gap between the interpole-piece4 and the frame-yoke i.

In accordance with my invention, however, a magnetizable flux-carryingpath of reduced section is provided, between each interpole-piece 4' andthe frame I, by means of oversized attachingboltsj H which pass throughthe frame-yoke l and into the interpole-piece 4 for holding theinterpole-piece in place. These holding-bolts 2|, of which there arepreferably two for each interpole-piece, are made of steel or othermagnetizable material, and provide a sufiicient cross-section to carrythe interpole flux for small-current conditions, say, up to 30 amperes,after which the shanks of these bolts, where they pass through thenon-magnetic spacer 20, become saturated, so as to begin to approach thesame effect as an air-gap. To compensate for this saturation and the airgap at the back of the interpole, I provide an abnormally large numberof turns on the interpole-windings 1, so as to overcompensate themachine until the bolts 2| become saturated, after which, with furtherincreases in load, the overcompensation decreases until, at some pointsuch as 162 amperes, the compensation is normal. The overcompensation atlight loads produces a circulating current in the short-circuitedarmaturecoils 9 which are undergoing commutation, and this circulatingcurrent has a cumulative series effect in increasing the flux throughthe main pole-pieces 2 under these light-load conditions.

The efi'ect of my special design-features in connection with the mainpole-piece 2 can be most readily understood by a study of the resultingfield-forms. Thus, in Fig. 2, I have shown, in the solid-line curve 23,the no-load field-form of the flux under a main pole-piece of a machinehaving a uniform air-gap and normal pole-tips which are close to thesaturation point when there is no armature reaction. When load comes on,I have assumed an armature-design and direction of rotation such as tohave the armaturereaction produce a cumulative magnetomotive force onthe right-hand side of the pole, and a differential magnetomotive forceon the left-hand side of the pole, as indicated by the dotted-line curveindicated at 24 in Fig. 2. It will be noted that the right-hand tipsaturates, so that there is very little increase in flux in it, whereasthere is a considerable decrease in the magnitude of the flux carried bythe left-hand pole tip, so that the over-all efi'ect is a reduction inthe flux carried by the pole-piece under loadconditions.

Fig. 3 shows similar curves for a machine hav ing a tapered air-gap suchas mine, but having normal pole-tips. Since the large air-gap under theright-hand tip reduces the flux-carried thereby, there is lesssaturation under no-load conditions. However, there is some saturationof the right-hand tip under load, with the result that the efiect of thearmature reaction is to decrease the flux carried by the mainpole-piece.

In Fig. 4, I show the efiect of .increasing the cross section of theright-hand pole-tip, while retaining the tapered air-gap and the normaldesign of the left-hand pole-tip. In this case, the result of thearmature reaction is to produce little, if any, change-in the total fluxcarried by the main pole-piece, there being possibly a slight in,-crease in the flux under load conditions.

In Fig. 5, I show the efiect of reducing the section of the left-handpole-tip so as to cause it to be saturated, even underload-conditions,whfle retaining the previously described unsaturated design of theright-hand pole-tip and the tapered air-gap. In this figure, it will beeasy to see that the saturated condition of the left-hand pole-tip 6prevents the armature reaction from reducing the flux as much as waspreviously the case, at the left-hand end ofthmpolepiece, while theunsaturated condition of the right-hand pole-tip permits a considerableincrease in the flux passl ing through the right-hand half of thepolepiece, with the result that there is a definite increase in theuseful exciting-flux of the machine, as a result of armature-reaction,with increasing loads.

1 The effect of an overcompensated interpoledesign at light loadsproduces a cumulative compounding efiect, as previously described, asthe result of the magnetizing armature-reaction of the circulatingcurrents which flow in the short- 20 circuited coils during commutation.In this manner, I am enabled to secure an additional increase in themain-pole flux as the result of the armature-reaction, particularly atthe light loads under the 30-ainpere value at which the inter- 25pole-bolts 2| begin to saturate. In this manner,

I am enabled to better maintain the required generator-voltage duringthe listening load-conditions when the generator is delivering itslightest load, of the order of 12 amperes.

80 Fig. 6 shows .the general combinations and connections of apower-plant including a generator, as above described, and a.prime-mover 3!, which will preferably have an approximately fiat, orslightly drooping, speed-characteristic with increased loads. Thepositive and negative generator-temnnal-leads are indicated at and Themain circuit may be traced from the negative lead through the seriesfield-coil 6, the armature 8 and the commutating coil 1, to

o the positive lead The shunt coil 5 is illustrated as being shuntedaround the armature 8 and the commutating or interpole-coil 1, althoughother excitation-means are known for the shunt coil. The shunt-coilexciting-current is regulat- 45 able by means of a field-rheostat 32.The series exciting coil 6 is connected so as to produce cumulativecompounding in an amount which is approximately correct to compensatefor the IR. drop due to the resistance or the main circuit 50 of thegenerator, and also to compensate for the slight droop in thespeed-characteristic of the prime mover ii. The compounding-efiect ofthe series winding 6 may be adjusted by means of an adjustableshunting-resistance 33 which is 55 connected therearound.

While I have illustrated my invention in a preferred form of embodiment,I wish it to be understood that various changes of omission,substitution or addition may be made by the skilled workers of the artwithout departing from some of the essential broader features of myinvention. I desire, therefore, that .the appended claims shall beaccorded the broadest construction consistent with their language andthe prior art. 65 I claim as my invention:

- 1. A self-regulating direct-current commutater-type generator or aspecial typ having a relatively flat voltage-characteristic from verylow loads up to somewhere in the order of 60% 70 of the normal loadwhich it may be called upon to carry, and a voltage-characteristic whichis drooping with increased load-current thereaiter, said generatorcomprising a field member comprising a yoke member, a plurality of mainpolepieces and a plurality of interpole-pieces, a rotor iace tip inwhich the armatur reaction produces 10 a differential magnetomotlveforce, the large end of the tapered air-gap being at the first tip, thefirst tip being of sufiicient cross-section to be substantiallyunsaturated for small load-currents, and the second .tip being of suchrestricted crosssections as to be substantially saturated at noload andat small load-currents.

2. A self-regulating direct-current commutator-typegenerator of aspecial type having a relatively fiat voltage-characteristic from verylow loads up to somewhere in the order of 60% of the normal load whichit may be called upon to carry, and a voltage-characteristic which isdrooping with increased load-current thereafter, said generatorcomprising a field member comprising a yoke member, a plurality of mainpolepieces and a plurality of lnterpole-pleces, a rotor membercomprising an armature core separated from the main pole-pieces andinterpole-pieces by air-gaps, a self-excited shunt coil on each mainpole-piece, and a series-connected interpolecoil on each interpolepiece,each main pole-piece having a pole-face with a tapered air-gap, and eachmain pole-piece having a first pole-face tip in which the armaturereaction produces a cumulative magnetomotive force and a second polefacetip in which the armature reaction produces a difierential magnetomotlveforce, the large end of the tapered air-gap being at the first tip, thefirst tip being of suflicient cross-section to be substantiallyunsaturated for small loadcurrents, the second tip being of suchrestricted cross-sections as to be substantially saturated at no-loadand at small load-currents, each interpole-piece including therein asection of such reduced cross-section as .to saturate at certain smallcurrents, and the interpole-coils being of such number of turns as toproduce overcompensation at all loads up to a certain predeterminedlarge load-current. 5e

3. A self-regulating direct-current commutator-type generatorot aspecial type having a relatively flat voltage-characteristic from verylow loads up to somewhere in-the'order of 60% or the normal load whichit may be called upon to carry, and a voltage-characteristic which isdrooping with increased load-current thereafter, said generatorcomprising a field member comprising a yoke member, a plurality of mainpolepieces and a plurality of interpole-pieces, a rotor membercomprising an armature core separated from the main pole-pieces andinterpole-pieces by air-gaps, a self-excited shunt coil and a cumulativeseries coil on each main pole-piece, and a series-connectedinterpole-coil on each interpolepiece, each main pole-piece having apole-face with a tapered air-gap, and each main pole-piece having afirst pole-face tip in which the armature reaction produces a cumulativemagnetomotive force and a second pole-race tip in which the armaturereaction produces a differential mags netomotive force, the large end ofthe tapered air-gap being at the first tip, the first tip being 0!sunicient cross-section to be substantially un; saturated forsmallload-currents, and the second tip being of such restrictedcross-sections as to be substantially saturated at no-load and at smallload-currents.

4. A self-regulating direct-current commutator-type generator of aspecial type having a relatively fiat voltage-characteristic from verylow loads up to samewhere in the order of of the normal load which itmay be called upon to carry, and a voltage-characteristic which isdrooping with increased load-current thereafter, said generatorcomprising a field member comprising a yoke member, a plurality of mainpolepieoes and a plurality of interpole-pieces, a rotor membercomprising an armature core separated from the main pole-pieces andinterpole-pieces by air-gaps, a self-excited shunt coil and a cumulativeseries coil on eachmain pole-piece, and a series-connectedinterpole-coil on each interpolepiece, each main pole-piece having apole-face witha tapered air-gap, and each main pole-piece having a firstpole-face tip in which the armature reaction produces a cumulativemagnetomotive force and a second pole-face tipin which the armaturereaction produces a differential magnetomotive force, the large end ofthe tapered air-gap being at the first tip, the first tip being ofsuificient cross-section to be substantially unsaturated for smallload-currents, the second tip being of such restricted cross-sections asto be substantially saturated at no-load and at small load-currents,each interpole-piece including therein a section of such reducedcross-section as to saturate at certain very small currents, and theinterpole-coils being of such number of turns as to produceovercompensation at all loads up to alargeload-current.

5. A power-planficomprising a prime-mover having a slightly droopingspeed-characteristic with increasing loads, and a self-regulatingdirect-current commutator-type generator, saidgenerator comprising afield member comprising a yoke member, a plurality of main pole-piecesand a plurality of interpole-pieces, a rotor member comprising anarmature core separated from the main pole-pieces and interpole-piecesby airgaps, a shunt coil and a cumulative series coil on each mainpole-piece, and a series-connected interpole-coil on eachinterpole-piece, each main pole-piece having a pole-face with a taperedairgap, and each main pole-piece having a first poleface tip in whichthe armature reaction produces a cumulative magnetomotive force and asecond pole-face tip in which the armature reaction produces adifierential magnetomotive force, the large end of the tapered air-gapbeing at the first tip, the first tip being of suflicient cross-sectionto be substantially unsaturated for small loadcurrents, the second tipbeing of such restricted cross-sections as to be substantiallysaturated'at no-load and at small load-currents, and the cumulativeseries coils having approximately the correct number of turns tocompensate for the armature resistance drop and the droop in thespeed-characteristics.

6. A power-plant comprising a prime-mover having a slightly droopingspeed-characteristic with increasing loads, and a self-regulatingdirect-current commutator-type generator, said generator comprising afield member comprising a yoke member, a plurality of main pole-piecesand a plurality of interpole-pieces, a rotor member comprising anarmature core separated from the main pole-pieces and interpole-piecesby airgaps, a self-excited shunt coil and a cumulative series coil oneach main pole-piece, and a seriesconnected interpole-coil on eachinterpole-piece,

' each main pole-piece having a pole-face with a tapered air-gap, andeach main pole-piece having a first pole-face tip in which the armaturereaction produces a cumulative magnetomotive force and a secondpole-face tip in which the armature reaction produces a difierentialmagnetomotive force, the large end of the tapered air-gap being at thefirst tip, the first tip being of sufficient cross-section to besubstantially unsaturated for small load-currents, the second tip beingof such restricted cross-sections as to be substantially saturated atno-load and at small load-currents, each interpole-piece including,therein a section of such reduced cross-section as to saturate atcertain very small currents, the interpole-coils being of such number ofturns as to produce overcompensation at all loads up to a largeloadcurrent, and the cumulative series coils having approximately thecorrect number of turns to compensate for the armature-resistance dropand the droop in the speed-characteristic.

ALBERT W. KIMBALL.

